1. Field
Embodiments of the present invention relate to an electromechanical brake system provided with a speed reducer having a function of changing speed, and may thereby improve responsiveness by changing the reduction ratio depending on the condition of load in braking of a vehicle.
2. Description of the Related Art
As vehicles are evolving from hybrid vehicles to electric vehicles through fast development of electronics, a hydraulic brake system is also converted into an electromechanical brake system for driving of a parking brake. Such an electromechanical brake system is mounted to a common disc brake to function as a parking brake.
FIG. 1 is a view showing an electronic disc brake adopting a conventional electromechanical brake system.
Referring to FIG. 1, the electromechanical brake system includes a disc 1 to rotate with a wheel of a vehicle, a base carrier 10 at which a pair of pad plates 11 and 12 disposed on both sides of the disc 1 to apply pressure to the disc 1 is installed, a caliper housing 20 slidably installed at the base carrier 10 for application of pressure to the pair of the pad plates 11 and 12, a motor 50 to produce driving force, a speed reducer 40 to amplify the driving force produced by the motor 50, and a pressing member 30 to covert rotational force of the motor 50 from the speed reducer 40 into rectilinear motion to apply pressure to the pad plate 11.
The pad plates 11 and 12 may be divided into an inner pad plate 11 adjacent to the pressing member 30, and an outer pad plate 12 positioned at the opposite side of the inner pad plate 11. A body 23 for installation of the pressing member 30 is provided at one side of the caliper housing 20, and a downwardly curved finger 22 integrally connected to the body 23 is provided at the other side of the caliper housing 20 to press the outer pad plate 12 against the disc 1 when the caliper housing 20 slides.
The base carrier 10 is fixed to a vehicle body to prevent separate of the pad plates 11 and 12 and to guide movement of the pad plates 11 and 12 toward and away from the disc 1.
The pressing member 30 is provided with a ball screw 32 screw-coupled to a central rotating shaft of a carrier 43 of the speed reducer 40, which is described below, to receive rotational force of the motor 50, and a ball nut 31 coupled to the ball screw 32 to apply pressure to the inner pad plate 11 with rectilinear motion. A bearing 25 is installed inside the body 23 to support the ball screw 32.
The speed reducer 40 includes a sun gear 41 installed at a rotating shaft of the motor 50, a plurality of planetary gears 42 disposed around the sun gear 41 to engage with the sun gear 41, an internal gear 44 fixed outside of the planetary gears 42 to engage with the planetary gears 42, and the carrier 43 to connect shafts 42a of the planetary gears 42 to the pressing member 30.
That is, in the case of the electromechanical brake system as above, when the sun gear 41 is rotated by operation of the motor 50, the planetary gears 42 engaged with the fixed internal gear 44 revolve about the internal gear 44. Revolution of the planetary gears 42 is transferred to the ball screw 32 via the carrier 43 to allow the ball screw 32 to rotate at a reduced speed. When the ball screw 32 rotates, the ball nut 31 axially moves, applying pressure to the inner pad plate 11 to perform braking.
However, when braking is performed using the electromechanical brake 10 as above, the planetary gears 42 in contact with the fixed internal gear 44 revolve. Revolution of the planetary gears 42 is transferred to the ball screw 32 via the carrier 43, thereby reducing the rate of rotation. That is, the conventional electromechanical brake system is provided with the speed reducer 40 which does not allow change of speed, and thereby responsiveness thereof is degraded in applying and releasing the brake and fast control may be not be implemented with the conventional electromechanical brake system.
In addition, as torque of the motor 50 is amplified to produce axial force, noise may be produced during braking.